Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual page 58

PSYCHROMETRIC CHART FUNDAMENTALS
Figure 18 is the same as the chart shown in Figure 17 except
that it graphically displays the amount of heat added by the
process. Enthalpy (total heat) added is determined by
subtracting the enthalpy of the dry, heated air at Point B from
the enthalpy of the humidified air at Point C as follows:
74.5 kJ/kg – 49.0 kJ/kg = 25.5 kilojoules per
The steam raised the temperature of the air from 32 C dry
bulb to 33 C dry bulb. To find the latent heat added by the
steam humidifier to the air, determine the enthalpy at Point D
(the enthalpy of the heated air without added moisture) and
subtract it from the enthalpy of the humidified air at Point C.
This is as follows:
74.5 kJ/kg – 49.8 kJ/kg = 24.7 kilojoules per
1.0
SENSIBLE HEAT
TOTAL HEAT
0
ENTHALPY
HUMIDITY RATIO
STEAM
ENTHALPY
2675 kJ/kg
kilogram of dry air
kilogram of dry air
REFERENCE POINT
1.0 -
H s
H t
TOTAL
ENTHALPY
h
W
LATENT
49.8
SENSIBLE
kJ/kg
(0.8 kJ/kg)
49
kJ/kg
A 13 C DB
The remaining 0.8 kJ/kg is sensible heat. The actual moisture
added per kilogram of dry air is 9.5 grams. The specific volume
of the entering air at Point B is 0.874 cubic meters per kilogram.
For a 4.72 cubic meters per Second system, the weight of the
air passing through is:
3
4.72 m /s 0.874 m
The weight of the moisture added is:
5.4 kg/s x 9.5 g/kg = 51.3 grams per second
74.5
kJ/kg
C
32 C DB B D
Fig. 18.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
48
3
/kg = 5.4 kilograms per
second
of moisture
50% RH
33 C DB
M15330
16 g/kg
6.5 g/kg